The energy crisis has led to the development of numerous surveys in order to recover a maximum amount of the oil present in the fields. Among the various considered methods, one of them consists of flooding the oil field by means of an injection of salt water in order to force petroleum out of the pores of the rock where it is adsorbed. However, the difference in mobility between oil and water considerably reduces the efficiency of said method. In order to improve this technique, it is known to thicken the injection water by means of hydrosoluble polymers, such as partially hydrolized polyacrylamides, acrylamide-sodium acrylate copolymers or polysaccharides:
On the other hand, it has been found that aqueous solutions, thickened by means of polymers, injected in wells simultaneously producing water and oil, limit the water production sufficiently without changing the oil production. However, the use of hydrosoluble polymers under actual conditions of use on the field, is often a delicate operation. As a matter of fact, the handling, storing and dissolution of polyacrylamides, as powder, gives rise to certain problems, particularly those due to absorption of moisture causing, formation of agglomerates, whose dissolution is time-consuming.
For this reason, new modes of conditioning hydrosoluble polymers have been proposed, particularly with inverse latices offering as a rule, all the advantages associated with liquids handling. In this connection U.S. Pat. Nos. 3,284,393, 3,624,019, 3,826,771 and 4,022,731, as well as German patent application No. DE-A-2.554.082 and British Pat. No. 2.030.578, are of particular interest.
In the formulations disclosed in these documents, the surfactant is most often selected from non-ionic surfactants having a low H L B (Hydrophilic Lipophilic Balance), providing a water-in-oil emulsion. It consists usually of a sorbitan monooleate or monostearate. On the other hand, it has been stated that certain surfactants of higher H L B are also liable to give water-in-oil emulsions (French Pat. No. 2 245 671).
However, inverse latices obtained according to the prior art methods suffer from different disadvantages, particularly an instability which results in a strong tendency to settle and in the requirement of intense and delicate shearing during their dissolution in aqueous phase, i.e. during their inversion.
More recently, it has been proposed to use inverse microlatices of hydrosoluble polymers of improved stability (French patent application No. 2 524 895), prepared by using anionic or cationic surface-active agents.